Lithographic product comprising lightsensitive diazido stilbene sulfonic acid salt



3,118,765 LITHOGRAPHIC PRODUCT COMPRISING LIGHT- gglEgITIVE DIAZIDO STILBENE SULFONIC ACID Robert F. Leonard, East Rockaway, and Madeline Beckett, Hempstead, N.Y., assignors to Litho Chemical and Supply Co., Inc., Lynbrook, Long Island, N.Y., a corporation of New York No Drawing. Filed Aug. 26, 1960, Ser. No. 52,030 6 Claims. (CI. 96-63) This invention relates to lithographic products and procedure and more particularly to products useful in connection with carrying out the deep etch process and to a new and useful photosensitive resist for use in such process.

The lithographic deep etch process is well known and widely practiced as particularly described in Publication No. 806 of the Lithographic Technical Foundation Inc. (1954). In this procedure a sheet of aluminum or zinc the surface of which has been suitably roughened or grained is freed of excess oxide and loose surface contamination by subjection to the action of a weak aqueous acidic solution.

This is sometimes referred to as counter-etching. Subsequently the aluminum or zinc sheet or plate is coated with a light-sensitive dichromated gum arabic solution and after drying the sheet or plate with its dried film of dichromated gum arabic is exposed to a light source through a photographic positive to harden those portions of the coating which have been subjected to the action of the light. Unexposed areas of the coating are developed or washed away with an aqueous acidic salt solution which does not attack the exposed areas of the coatmg.

At this stage the plate or sheet consists of a light hardened dichromated gum arable stencil with bare metal image areas. Deep etching of the plate or sheet is then carried out by treatment with a suitable acidic salt solution that etches the metal to a depth of .0002" to .0003" but does not attack the stencil.

The plate or sheet is then flushed with an anhydrous alcohol to remove both the salts and the moisture of the deep etch solution. In an optional procedure the plate or sheet is treated with a copper salt solution which chemically deposits a film of metallic copper on the etched image areas. This step is followed by a further alcohol wash.

The thus treated sheet or plate is fanned dry and coated with a thin film of a lacquer which is also fanned dry and thereafter a thin film of developing ink is applied to the sheet or plate surface and fanned dry.

The hardened dichromated gum arabie stencil together with the lacquer and developing ink adhering thereto is removed by soaking in warm Water while the lacquer and developing ink remain on the etched portions which constitute the image areas of the sheet or plate.

After drying, the sheet or plate is then ready for use. The particular material of the solutions and the conditions for carrying out the foregoing steps are set forth in the said Publication 806 and are incorporated herein by reference.

While only gum arable sensitized with dichromate is referred to above, it is to be understood that various other natural colloids such as gelatin, fish glue, egg albumen, soya bean protein and shellac have been heretofore employed. All these natural colloids have the common disadvantage that they are variable in chemical and physical properties and consequently yield lithographic printing materials which show variations in use. This is recognized as being a serious disadvantage which has not heretofore been satisfactorily overcome. Moreover, the

nited States Patent 'ice permissible time lapse between coating the sheet or plate with these materials and exposing it to a light source is relatively short and a much greater range of applications could be realized if a longer, effective, usable period between coating and exposure to light could be utilized.

The standard dichromated gum arabic solutions have only a comparatively short storage life due to the fact that crystallization in the solution gradually occurs and is clearly apparent two or three months after preparation.

Another important consideration is that precoating of sensitized plates cannot be carried out under commercial conditions when the life of such plates is only a few days. The sensitivity of such plates varies with their age due to the progressive action of the dichromate on the colloid even in the absence of light and an exposed plate of dichromated gelatin or gum arabic undergoes progressive hardening, with the result that exposed plates must usually be developed promptly after exposure if consistent results of the best quality are to be obtained.

An inherent objection and disadvantage to the use of a natural colloid is based upon the dependency for such colloid upon natural products grown and supplied abroad and untable or unfavorable conditions make it uncertain as to whether a constant supply of a satisfactory product can be maintained at a suitable price.

It would therefore be much better if a synthetic product were used which could be manufactured locally under such conditions that a uniform high grade product could always be depended upon.

The major object of the present invention is to improve the standard form of deep etch process as particularly applied to aluminum and zinc sheets or plates and to overcome the drawback and disadvantages of the existing process as outlined above.

Another and more specific object of the invention is to provide a synthetic material which can be manufactured wherever desired and of uniform high quality to take the place of the natural colloids mentioned above.

Other and further objects and advantages reside in the particular chemical compositions and procedural steps hereinafter described.

According to the present invention and referring to the new chemical composition to replace the natural colloids heretofore used in the deep etch lithographic process, it has been found that the reaction product of polyacrylic acid and polyvinyl pyrrolidone when used in conjunction with a suitable diazonium compound pro duces a light-sensitive product which is ideally suited as a deep etch resist.

This new composition consisting of the reaction product of polyacrylie acid and polyvinylpyrrolidone together with a suitable diazonium compound overcomes all the disadvantages noted above with respect to the presently employed resists.

This new composition is characterized by the fact that the raw or starting materials being of synthetic nature can be accurately controlled with required tolerances. This sensitizied resist is superior to the resists of the prior art due to longer useful life in solution and as an exposed or unexposed coating as it retains substantially the same sensitivity over a prolonged period of time.

It will be appreciated that this is especially important in step-and-repeat work as no compensation need be made in the exposure from the beginning to the end of the procedure. From this comes the additional advantage that work on a sheet or plate no longer has to be completed on the day that it was started or on any particular day as it is even possible to begin work on a step-and-repeat sheet or plate at the end of a week and to continue and complete the work after the weekend.

These extremely important characteristic advantages of the new composition or reaction product have not heretofore been obtainable in any known or practical manner.

,It is recognized that polyvinylpyrrolidone has previously been utilized in conjunction with diazonium sensitizers pyrrolidone both in water and in organic solvents. This shortcoming has been overcome by the present invention due to the formation of a reaction product between polyacrylic acid and the polyvinylpyrrolidone since the reaction product has the requisite solubility characteristics necessary for a deep etch resist.

'In] preparing the new reaction product or composition, it has been found to be best from a lithographic standpoint to have the polyvinylpyrrolidone with a K value between 88 and 94, K values assigned to various grades of polyvinylpyrrolidone representing a function of the mean molecular weight. For example, pol-yvinylpyrrolidone K-90 has an average molecular weight of 360,000.

The polyacrylic acid used is manufactured and sold under the name of Good-rite K-702 Polymer and is a 25% aqueous solution of polyacrylic acid. Such solution has a viscosity of 500 to 1200 c.p.s., a specific gravity of 1.09, and a pH value of 2 to 3.

Its molecular weight is in the range of 90,000 to 100,000.,

The diazonium sensitizer is 4,4'-diazidostilbene-2,2-disulfonic'acid sodium salt and is produced by diazotizing 4,4':diaminostilbene-2,2'-disulfonic acid and neutralizing the reaction product by sodium carbonate. Sodium azide is then "added to yield the tetrazo form of the above compound and'this last step has the significance of increasing the hardening action of the diazo upon the polyacrylic acidpolyvinylpyrrolidone reaction product.

I A typical formulation according to the invention is Percent by weight Water (distilled) 94.25 Polyvinylpyrrolidone K-90 4.09 Polyacrylic acid, M.W. 95,000 0.23 Sodium salt of 4,4'-diazidost-ilbene-2-2' disulfonic acid 0.91 Sodium azide 0.30 Octyl phenoxy polyethoxy ethanol having an ethoxy chain of 9 to 11 carbon atoms 0.22

The octyl phenoxy polyethoxy ethanol has an ethoxy chain length of 9 to 11 carbon atoms and is a wetting agent manufactured and sold under the name of Triton X- 100, but it is to be understood that an other suitable wetting agent may be used instead of the Triton X-100.

The proportions in the foregoing formulation are of critical significance and must not vary appreciably above or below the percentages specified except that it is permissible to vary the percentage of each of the above constituents up to 10% above or below the percentages set forth without adversely affecting the working properties of the deep etch positive senstizer to any appreciable extent, but beyond this 10% deviation the working properties of the deep etch positive sensitizer will be adversely affected.

The invention is illustrated by the following non-limitative examples:

Example I A 17" x 22" x 0.012" sheet of ball grained 28 alloy aluminum is counteretched with a dilute aqueous solution of acetic acid and then rinsed thoroughly with tap water. The aluminum sheet is whirl coated with the deep etch positive sensitizer described above using conventional equipment and procedure. The sheet, after having been whirled dry, is exposed to a 13-amp. single carbon arc lamp at a distance of 40" for minutes through a photographic positive. The sheet is then developed with the following developing solution which selectively dissolves the non-light struck portions of the coating:

Grams Water 32.88 CaCl 13.78 ZnCl 11.85 Hydroxyacetic acid 1.64 Ethylene glycol 39.84

CaClsolution aqueous (4041 B) ml 1000 ZnCl, grams 380 FeCl solution aqueous (5051 B) ml 285 HCl solution (37-38%) aqueous ml 14 CuCl lH O grams 27 The sheet is next washed with 99% isopropyl alcohol to remove the etching solution after the desired depth of etch has been reached. The plate is now treated with a solution which will chemically deposit copper metal onto the bare etched image areas. The composition of such a copperizing solution is:

isopropyl alcohol (99%) ml 1000 Cuprous chloride (Cu Cl grams 31 HCl (37-38.5%) ml 32 The plate is again flushed with 99% isopropyl alcohol to remove the copperizing solution and to assist in regtoving moisture from the sheet surface which is fanned Next the sheet is coated with any of the commercial non-blinding deep etch lacquers which are usually vinyl based. The lacquering step is followed by an inking step which comprises coating the plate with a layer of commercial developing ink. The purpose of this step is to make the image apparent and to protect the lacquer layer from chemical attack. The plate is then flushed with warm water and brushed lightly to remove the resist and the lacquer and ink adhering thereto.

Thereafter the plate is desensitized by coating with a solution of phosphoric acid and gum arabic and when dried, moistened and inked, it is ready for printing.

Example II A 17" x 22" X 0.009" sheet of ball grained zinc is counteretched with a dilute aqueous solution of hydrochloric acid, then rinsed thoroughly with tap water. The zinc sheet is whirl coated with the deep etch positive sensitizer described above, using conventional equipment and procedure. The sheet, after having been whirled dry, is exposed to a 13 amp single carbon, are lamp at a distance of 40" for 5 minutes through a photographic positive. The sheet is then developed with the following developing solution which selectively dissolves the non-light struck portions of the coating.

Grams Water 32.88 CaCl 13.78 Znci 11.85 Hydroxyaeetic acid (100%) 1.64 Ethylene glycol 39.84

The spent developing solution is removed from the plate with simultaneous removal of unhardened portions of the coating, after which the plate is ready for deep etching. The etching of the plate is accomplished by treating the unprotected portions thereof with the following ctching solution:

Grams Water 45.99 CaCl 34.43 MgCl 15.30 Lactic acid (100%) 1.37 Formic acid (100%) 2.91

The sheet is next Washed with 99% isopropyl alcohol to remove the etching solution after the desired depth of etch has been reached. The plate is now treated with a solution which will chemically deposit copper metal onto the bare, etched image areas. The composition of such a copperizing solution is:

Isopropyl alcohol (99%) ml 1000 Cuprous chloride (Cu CI "grams" 31 HCl (37.38%) aqueous solution ml 32 The plate is again flushed with 99% isopropyl alcohol to remove the copperizing solution and to assist in removing moisture from the sheet surface which is fanned dry.

Next, the sheet is coated with any of the commercial non-blinding deep etch lacquers which are usually vinyl based. The lacquering step is followed by an inking step which comprises coating the plate with a layer of commercial developing ink. The purpose of this step is to make the image apparent and to protect the lacquer layer from chemical attack. The plate is then flushed with warm water and brushed lightly to remove the resist and the lacquer and ink adhering thereto.

Thereafter the plate is desensitized by coating it with a solution of phosphoric acid and gum arabic and when dried, moistened and inked, it is ready for printing.

The polyarcylie acid-polyvinylpyrrolidone reaction product is new and useful in the lithographic field particularly for the production of a deep etch resist upon admixture with the diazonium sensitizer. While this has been found to be particularly valuable in the lithographic field, it has other application as in the fields of photoengraving and chemical milling. The invention comprises not only such reaction product and diazonium compound composition therewith but also the procedure for producing a lithographic sheet ready for printing.

What is claimed is:

1. A deep etch positive sensitizer lithographic composition comprising 0.23 percent of polyacrylic acid and 4.09 percent of polyvinylpyrrolidone admixed with 0.91 percent of the sodium salt of 4,4 diazidostilbene-2,2'- disulfonic acid as a diazonium sensitizer and 0.30 percent of sodium azide, the polyacrylic acid having a molecular weight of 90,000 to 100,000 and the polyvinylpyrrolidone having an initial K value between 88 and 94, the balance of the composition being substantially all water, all percentages being by weight of the composition and being variable only within percent of the said values.

2. A composition according to claim 1, in which 0.22 percent of a wetting agent is incorporated.

3. A deep etch positive sensitizer having the following approximate formulation by weight: water 94.25 percent, the admixture product of 4.09 percent of polyvinylpyrethoxy ethanol having an ethoxy chain length of 9 to 11 carbon atoms, the said percentages being variable only within 10 percent of said values.

4. In a process for producing a deep etch lithographic plate, the surface of which has been counter etched and rinsed with water, the steps that comprise applying to the thus treated plate by whirl coating the sensitizer of claim 1 and then whirl drying the resulting coated plate.

5. In a process for producing a deep etch lithographic plate, the surface of which has been counter etched and rinsed with water, the steps that comprise applying to the thus treated plate by whirl coating the sensitizer of claim 3 and then whirl drying the resulting coated plate.

6. In a process for producing a deep etch lithographic plateformed from a surface-roughened sheet selected from the group consisting of aluminum and Zinc, the steps that comprise applying to such sheet by whirl coating the sensitizer of claim 3, whirl drying the coated sheet, developing it after exposure through a photographic positive with a developing solution which selectively dissolves the non-lightstruck portions, etching the sheet, treating it with a copperizing solution and lacquering and inking it, whereupon the thus treated sheet is desensitized and made ready for printing, the developing solution having the following aproximate formulation:

grams Water 32.28 CaC1 13.78 ZnCl 11.85 Hydroxyacetic acid 1.64 Eethylene glycol 39.84

References Cited in the file of this patent UNITED STATES PATENTS 2,220,252 Loefiler Nov. 5, 1940 2,564,414 Whyzmuzis et al Aug. 14, 1951 2,676,886 Barbarite Apr. 27, 1954 2,678,275 Leekley May 11, 1954 2,687,958 Neugebauer Aug. 31, 1954 2,692,826 Neugebauer et a1 Oct. 26, 1954 2,853,465 Werner Sept. 23, 1958 2,901,457 Stoner et a1 Aug. 25, 1959 2,910,358 Coles Oct. 27, 1959 2,942,974 Schwarz June 28, 1960 2,971,937 Ham et a1. Feb. 14, 1961 FOREIGN PATENTS 449,772 Great Britain July 2, 1936 888,805 Germany Sept. 3, 1953 QTHER REFERENCES Chemistry of Lithography, Lithographic Technical Foundation, New York, 1952, page 139. Mertle et al.: Photomechanics and Printing, Mertle Publishing Co., Chicago, 1957, page 297.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3, 118,, 765 January 21, 1964 Robert FD Leonard et a1,

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 23, for "untable" read unstable column 5, line 34, for "polyarcylic" read polyacrylic column 6, line 32, for "32,28" read 32.188 line 36,

for "Eethylene" read Ethylene n Signed and sealed this 16th day of June 1964) (SEAL) Attest:

ERNEST W. SWIDER EDWARD J BRENNER Attesting Officer Commissioner of Patents 

3. A DEEP ETCH POSITIVE SENSITIZER HAVING THE FOLLOWING APPROXIMATE FORMULATION BY WEIGHT: WATER 94.25 PERCENT, THE ADMIXTURE PRODUCT OF 4.09 PERCENT OF POLYVINYLPYRROLIDONE HAVING A K VALUE OF 90 AND 0.23 PERCENT OF POLYACRLIC ACID HAVING A MOLECULAR WEIGHT OF 95,000, THE TETRAZO FORM OF 0.91 PERCENT OF THE SODIUM SALT OF 4,4''-DIAZIDOSTILBENE-2,2''-DISULFONIC ACID WITH 0.30 PERCENT OF SODIUM AZIDE, AND 0.22 PERCENT OF OCTYL PHENOXY POLYETHOXY EHTANOL HAVING AN ETHOXY CHAIN LENGTH OF 9 TO 11 CARBON ATOMS, THE SAID PERCENTAGES BEING VARIABLE ONLY WITHIN 10 PERCENT OF SAID VALUES.
 6. IN A PROCESS FOR PRODUCING A DEEP ETCH LITHOGRAPHIC PLATE FORMED FROM A SURFACE-ROUGHENED SHEET SELECTED FROM THE GROUP CONSISTING OF ALUMINUM AND ZINC, THE STEPS THAT COMPRISE APPLYING TO SUCH SHEET BY WHIRL COATING THE SENSITIZER OF CLAIM 3, WHIRL DRYING THE COATED SHEET, DEVELOPING IT AFTER EXPOSURE THROUGH A PHOTOGRAPHIC POSITIVE WITH A DEVELOPING SOLUTION WHICH SELECTIVELY DISSOLVES THE NON-LIGHTSTRUCK PORTIONS, ETCHING THE SHEET, TREATING IT WITH A COPPERIZING SOLUTION AND LACQUERING AND INKING IT, WHEREUPON THE THUS TREATED SHEET IS DESENITIZED AND MADE READY FOR PRINTING, THE DEVELOPING SOLUTION HAVING THE FOLLOWING APPROXIMATE FORMULATION: 